1. Field of the Invention
The present invention relates to a post-processing device for applying a post-process to one or more sheets fed thereinto, and an image forming apparatus.
2. Description of the Related Art
An image forming apparatus for printing an image onto a sheet (paper), e.g., a printer, a copier, or a Multi-functional Peripheral (MFP), is provided with a sheet containing portion in which lots of sheets of paper are loadable and from which the paper is supplied. Such an image forming apparatus carries out printing while supplying the sheets one by one from the sheet containing portion and conveying the sheets.
The image forming apparatus is internally or externally provided with a post-processing device for applying a post-process to a sheet on which an image has been printed. The post-processing device has at least a function to apply a post-process called “alignment process” of aligning stacked sheets of paper. There has been known a post-processing device for applying a post-process such as stapling the sheets that have been subjected to the alignment process, or punching a hole in the sheets that have been subjected to the alignment process.
For execution of a print job, the image forming apparatus timely gives the post-processing device information related to the post-process. For example, before starting to execute the print job, the image forming apparatus informs the post-processing device of the details of settings such as the number of prints, the set of prints, paper size designated by a user, and post-process to be applied (the necessity or lack of necessity of stapling, for example). During execution of the print job, when a sheet is conveyed to a predetermined position on a paper-transfer path from the sheet containing portion for paper feed through a print position to the post-processing device, the image forming apparatus informs the post-processing device of the fact. The post-processing device applies, based on the given information, the post-process to sheets which have been subjected to the print process and are sequentially fed thereinto at an appropriate time synchronously with the paper feed.
A technology related to operation of the post-processing device has been proposed. According to the technology, the speed of operation for discharging a sheet externally from the post-processing device is controlled depending on the sheet size and the number of sheets. This secures the alignment of sheets discharged externally (Japanese Laid-open Patent Publication No. 2007-145528).
Suppose that print jobs are entered one after another into the image forming apparatus. In such a case, while the post-processing device applies a post-process to one or more sheets related to a preceding print job, a sheet related to the next print job sometimes cannot be fed into the post-processing device. This needs sheet conveyance related to a subsequent print job to be delayed in such a manner that the sheet conveyance is started after the post-processing device is ready to receive the sheet related to the next print job. The delay in sheet conveyance lowers the printing productivity of the image forming apparatus.